1. Technical Field of the Invention
The present invention relates to a cement burning apparatus capable of safely and efficiently drying high-water-content organic waste such as high-water-content organic sludge and a method of drying high-water-content organic waste utilizing the apparatus.
2. Description of the Related Art
Conventionally, variety of apparatus and methods for treating waste such as city garbage in cement burning apparatus has been proposed. For instance, in the patent document 1 is disclosed a technology, in which a part of hot air from a clinker cooler is introduced to a dryer for drying waste such as city garbage; gas exhausted from the dryer is returned to the clinker cooler; and the hot air, with which the exhaust gas is mixed, from the clinker cooler is used as air for combustion in a cement kiln or a calciner.
Further, in the patent document 2, a technology for burning combustible waste in cement burning apparatus is disclosed. In this technology, combustible waste is burned with a part of hot air from a clinker cooler; exhaust gas generated in a waste burning process is aerated to a preheater for heating cement raw material; and sludge generated in the waste burning process is extracted.
However, as described in the above patent documents, the hot air extracted from the clinker cooler can be utilized for drying waste such as city garbage, combustible waste and the like without causing any trouble, but when the hot air is utilized for drying high-water-content organic waste such as high-water-content-organic sludge, oxygen concentration of the hot air is high so that there is a danger of explosion.
In addition, even if combustion exhaust gas downstream from the exit of a preheater of a cement burning apparatus was tried to be utilized, since temperature of the combustion exhaust gas in the range was low, that is, 450° C. or less, the gas would not be suitable to dry the high-water-content sludge. On the other hand, gas extracted from the inlet end of a cement kiln is low in oxygen concentration and high in temperature, that is, approximately 1000° C., so that it is suitable to dry the high-water-content organic waste, but extraction of the combustion gas from the inlet end causes a problem that thermal efficiency of the cement kiln decreases.
In consideration of the above problems, the present applicant has eagerly investigated and found that oxygen concentration of the combustion gas extracted from the exhaust gas passage, which runs from the outlet duct of the calciner to the outlet duct of the preheater of the cement kiln is low, that is, 2 to 8 percent, so that there is no danger of explosion, and since temperature of the combustion gas is 450 to 900° C., the high-water-content organic waste can sufficiently be dried and combustion gas is not extracted from the inlet end or the like of the cement kiln, which does not decrease thermal efficiency of the cement kiln.
Patent document 1: Japanese Patent Publication Showa 63-151650 gazette
Patent document 2: Japanese Patent Publication 2003-506299 gazette
As described above, in order to dry high-water-content sludge etc., the combustion gas extracted from the exhaust gas passage, which runs from the outlet duct of the calciner to the outlet duct of the preheater of the cement kiln, can be used. But, the gas exhausted from the cement kiln as a hot source gas for drying contains incombustible dust derived from cement raw material, and most of the dust is recovered in dried sludge. In addition, dust concentration of the cement kiln exhaust gas is between approximately 0.05 kg/Nm3 (at an outlet portion of the highest cyclone) and approximately 1.0 kg/Nm3 (at an inlet portion of each cyclone), which means that the concentration considerably varies with area from which the combustion gas is extracted.
Here, the dried sludge containing dust derived from cement raw material has advantages and disadvantages. An advantage is that the dried sludge containing incombustible dust reduces danger of explosion at a facility for drying. On the contrary, a disadvantage is that the dried sludge containing incombustible dust reduces value of the dried sludge as a fuel.
In addition to the above, the high-water-content organic sludge shapes clumps including 40 mass percent of water or more like clay and its specific surface area is small, which makes it difficult to efficiently dry the organic sludge.
The present invention has been made in consideration of the above problems in the conventional art, and the object thereof is to provide a cement burning apparatus and a method of drying high-water-content organic waste reducing the danger of explosion at the facility for drying; not causing decreased value of the dried sludge as a fuel; and efficiently drying high-water-content organic waste.